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Old 25th November 2007, 01:20 AM   #1531
DaveM is offline DaveM  United States
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So, the new parts are in and the story is the same. 155 mV max bias with no DC offset. I'm stumped, but not giving up. The mosfest I am using were matched by Peter Daniel. Now unless I somehow shuffled them, I think they should be ok.

Winter is coming..... Ha!! We've had snow twice. We actually had snow and then the last of the trees in our yard dropped the leaves. I spent part of today raking frozen wet leaves.

I am going to work on walls before that bass horn, yet I may end up there someday.
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Old 25th November 2007, 01:35 AM   #1532
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How about something like this?
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Old 25th November 2007, 01:37 AM   #1533
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Quote:
Originally posted by DaveM
So, the new parts are in and the story is the same. 155 mV max bias with no DC offset.

This is with 8k on R9?, try going down a smidgen, like 7k. You're so close!
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Old 25th November 2007, 01:53 AM   #1534
Variac is offline Variac  United States
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I'm another of the winter F4 Improvement Society. Also rebuilding to a new system, F4 based. I DO have an advantage as my F4's have been operational- I just need to strip them down and rebuild them to be reliable. Then I have actually just ordered a kit for a Pumpkin pre. Finally a balanced Twisted Pear DAC and my old Baszilla's ....and time for a break - I hope before winter is over....
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Old 25th November 2007, 02:42 AM   #1535
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Hi Variac,

Which F4 version do you own? Maybe Dave can compare some setting with you?
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Old 25th November 2007, 02:55 AM   #1536
jleaman is offline jleaman  Belgium
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My F4 amp is for sale, nothing wrong with it, but i don't need it. I hve 4 aleph's Any one want a 90% completed amp ? Needs face plate and rear plate and top.
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Old 25th November 2007, 03:17 AM   #1537
DaveM is offline DaveM  United States
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So, I believe that we are barking up the wrong tree with changes to R9. Every change I make I am able to dial right back to 160 mV bias and no DC offset with P2 at zero.

Is there any harm in dropping R22 down so that I have more bias adjustment?
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Old 25th November 2007, 03:37 AM   #1538
BDP is offline BDP  United States
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By any chance did you measure each source resistors voltage?
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Old 25th November 2007, 03:39 AM   #1539
DaveM is offline DaveM  United States
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Yes I did. There is slight variation, but they are very close. +/-1 mV
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Old 25th November 2007, 04:07 AM   #1540
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Quote:
Originally posted by DaveM

Is there any harm in dropping R22 down so that I have more bias adjustment?

Sure, I'd take a chance, but make a subtle change. If things work in your favor, continue--less chance of letting out the magic smoke.

Also, describe your P1/P2 adjustment process, please.

You're using 1N4736 diodes?
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